late 14c. as a term in astronomy, from Old French depression (14c.) or directly from Latin depressionem (nominative depressio), noun of action from past participle stem of deprimere "to press down, depress" (see depress).
Attested from 1650s in the literal sense; meaning "dejection, depression of spirits" is from early 15c. (as a clinical term in psychology, from 1905); meteorological sense is from 1881 (in reference to barometric pressure); meaning "a lowering or reduction in economic activity" was in use by 1826; given a specific application (with capital D-) by 1934 to the one that began worldwide in 1929. For "melancholy, depression" an Old English word was grevoushede.
depression de·pres·sion (dĭ-prěsh'ən)
The act of depressing or the state of being depressed.
A reduction in physiological vigor or activity.
A lowering in amount, degree, or position.
An inward displacement of a body part.
A hollow or sunken area.
The condition of feeling sad or despondent.
A psychotic or neurotic condition characterized by an inability to concentrate, insomnia, and feelings of extreme sadness, dejection, and hopelessness.
A period of drastic decline in the national economy, characterized by decreasing business activity, falling prices, and unemployment. The best known of such periods is the Great Depression, which occurred in the 1930s.